1. Field of the Invention
The present invention relates to a device for the application of a liquid medium onto a moving material web, and, more particularly to the application of a liquid medium onto a moving cardboard web.
2. Description of the Related Art
The Voith publication p 2745, FIG. 1 describes a so-called size press. The size press includes two parallel rolls that form a nip through which the paper web travels. There is a liquid sump between the web and each of the two rolls, so that the web is impregnated simultaneously from both sides during operation. This device has the disadvantage that, with increasing web speed, the liquid in the sump is subject to very high turbulence, causing the liquid to splash into the surrounding area, for example onto device components and onto the web. Such splashing precludes a uniform application of liquid onto the web.
An attempt was made, with the device described in DE 29513970, to avoid splashing with the help of displacers or stabilizers. However, the device described in DE 29513970, has not proven completely satisfactory during operation.
Coating medium feed devices that dip into the sump are known from DE 29610446. A method and a device including a feed device, that dips into the sump, is also known from U.S. Pat. No. 4,358,484 and U.S. Pat. No. 4,407,224. In each case the feed device includes a main distributor tube that is equipped with delivery openings along its entire length. These delivery openings are connected with a flow channel for the formation of the sump. The flow channel is part of a nozzle body. The nozzle body includes parallel walls, extending across the entire width of the feed device Nozzle lips, that are located on these parallel walls, dip into the sump. The nozzle body is divided, in its center, by a wall into the aforementioned flow channel in order to supply the sump, and into another channel, which discharges the coating medium, of the sump, by way of vacuum, in order to create a reservoir. The arrangement thus described is a loop, in which coating medium is supplied from the reservoir to the sump, and it is again discharged.
It is the intent of these solutions to keep the depth of the sump as low as possible in order to avoid splashing and significant turbulence.
However, the design of these devices is relatively expensive, since there is a collection chamber at the discharge channel from which the medium must be pumped into the reservoir. Moreover, the entire device is permanently installed. In the event of a roll change the entire device must be dismantled, which is very labor and cost intensive.
The present invention provides an improved application device that includes ease of cleaning, ease of operation and ease of adaptation to specific application situations, at the same time largely avoiding splashing from the sump.
The inventor has recognized that, considering the current high operating and web speeds, the depth of the sump is not the decisive factor for a splash-free operation and a uniform coating application, but rather, that it is necessary to reduce the sump surface area.
Contrary to the teachings of the related art, it is even advantageous to let the sump level rise. This achieves a longer dwell time of the web in the sump, without causing saturating and/or breaking of the web, resulting in better penetration and uniformity of the coating application.
The desired dimension of the open sump surface can be adjusted by special nozzle lips, which are selected from a modular system and are matched precisely to the sump cross section, in shape and size. The nozzle lips are manufactured from a synthetic material. They can easily be manufactured in any desired shape and size and can easily be screwed or clipped onto the walls of the nozzle body.
During trials an immersion depth of up to approximately 80% of the height (or length) of the nozzle lips has proven to be the most effective, in avoiding splashing and unevenness in the application, and impregnation of the web.
It is especially advantageous if the entire delivery device is connected with a pivoting device. This arrangement allows the delivery device to be pivoted from the nip so that on the one hand, sufficient space remains to clean the roll, or rolls and on the other hand, the device need not be removed if one or both rolls need to be replaced. The pivoting arrangement is supported separately from the roll supports, in order to accommodate the last cited advantage.
Another, advantage of the device, in accordance with the present invention, is related to the structural shape of the nozzle body. The nozzle body is kinked or bent, starting from the nip, toward the outside. The shape of the nozzle body is chosen to compliment the shape of the roll. The lower section of the nozzle body is also matched to the form of the gusset, which is filled by the sump, existing between the roll and the supported, moving material web. It is also conceivable that the nozzle body is equipped with a joint, so that the desired deflection angle can be adjusted.
This aforementioned structural shape has an additional advantage in that the device is very compact. It distinguishes itself through a low construction height, which allows an operator a clear view of the roll, or rolls of the so-called size press or film press.
With regard to operational safety, the entire design offers a particularly effective nip protection for the operating personnel.
It must also mentioned that, for the purpose of a one-sided application, the applicator device is located and active only on one side. For the purpose of a two-sided application, application devices are located on both sides of the material web. Mention must also be made of the fact that, in place of the rolls, other types of support elements may be utilized, for example, moving flexible continuous belts.
It is effective if the nozzle, that is formed by the lips of the nozzle body, discharges the coating medium, that is supplied to the sump directly, downwardly, that is in the direction of the gusset tip. This ensures that the coating medium reaches the lowest point of the gusset and can therefore, be pressed reliably into the material web in the nip.
The medium discharging from the nozzle, the rolls or the support belts and also the moving material web have the same direction of travel. However, vortex formation can occur at especially high operating speeds, thereby possibly negatively influencing the coating application results. Another effective solution lies in the formation of the nozzle as a baffle nozzle. By locating a baffle-strip a small distance below the discharge opening, the arriving coating medium is redirected in a radial direction. The created cross flows reduce the undesirable vortex formation.